Fluid streams are often shielded from their surrounding environments to prevent contamination in many industrial processes. The shielding is normally carried out by surrounding the fluid streams with a shielding fluid, such as an inert gas. The shielding fluid, in turn, prevents reactive gases, such as oxygen, in the fluid streams' surrounding environments from infiltrating into the fluid streams.
U.S. Pat. No. 3,470,347 discloses a method for producing a substantially oxygen-free coating on a substrate by the use of a plasma arc coating torch. The torch produces an arc plasma through a constricting nozzle orifice so as to provide a high velocity, high energy arc effluent which carries coating materials to be deposited onto the substrate. The effluent is protected from its surrounding environment by surrounding it with a uniform turbulent flow of a coaxial annular shielding gas stream having a certain width and a certain forward momentum. The coaxial annular shielding gas stream, however, can only protect the effluent containing coating materials for a short distance. When the substrate to be coated is located too far from the torch, the coating materials in the effluent are oxidized before they are deposited on the substrate. Moreover, such a coaxial annular shielding stream according to U.S. Pat. No. 5,154,354 is susceptible to disruption by local cross winds. Disruption of the flow of the shielding gas allows air to infiltrate into the effluent and to oxidize the coating materials therein to cause an unsatisfactory quality of coating. In addition, this coaxial flow of the shielding gas does not block the ultra violet light given out by the effluent (plasma stream). The ultra violet light can cause blindness and produce ozone in the ambient air. Furthermore, this shielding arrangement is not effective for certain plasma deposition applications. For example, a low temperature melting material, such as plastic powder, may be used to coat a substrate. This material needs to be blown into the effluent of the torch through a tube as the effluent emerges from the nozzle in order to prevent overheating of the material. However, blowing the material, as well as the tube, disrupts and/or blocks the flow of the coaxial annular shielding gas and causes the effluent to be unprotected.
U.S. Pat. No. 4,869,936 discloses a method for shielding a particle-carrying high velocity oxyfuel flame stream. The shielding method involves ejecting the particle-carrying high velocity oxyfuel flame stream into a shielding cylinder and using a plurality of nozzles to produce a high velocity tangential flow around the particle-carrying high velocity oxyfuel flame stream within the shielding cylinder. The shielding cylinder, however, may fail after a short period of operation due to the combination of high temperature and high gas velocity. This may necessitate frequent shut downs to replace the shielding cylinder.
U.S. Pat. No. 4,992,337 discloses an electric arc spray process for the deposition of reactive metals. The reactive metals are sprayed from the electric arc with compressed inert atomizing gases. The sprayed reactive metals, however, would be rapidly mixed with air and would experience some oxidation before being deposited on a substrate. This process is not effective for shielding, among other things, plasma arc sprays, gas atomization of molten metals or high velocity oxyfuel flame streams.
Accordingly, it is an object of the invention to provide systems and processes for shielding turbulent fluid effectively in an efficient manner.
It is another object of the invention to provide systems and processes useful for blocking most of the ultra violet light given off by very high temperature turbulent gas streams.
It is yet another object of the invention to provide systems and processes for effectively depositing coating materials on different size substrates located at various distances from a torch or a nozzle for ejecting a turbulent fluid stream.
It is an additional object of the invention to provide shielding systems which can be retrofitted easily on existing spray devices, without any water cooling or other external cooling.
It is a further object of the invention to provide shielding systems that can be used with a tube or other solid objects which is located downstream of a turbulent fluid stream.